In recent years, an increasing effort has been devoted to identify new and effective ways to use renewable feedstocks for the production of organic chemicals. Among a plethora of downstream chemical processing technologies, the conversion of biomass-derived sugars to value-added chemicals is considered very important. In particular, six-carboned carbohydrates, i.e. hexoses such as fructose and glucose, are widely recognized the most abundant monosaccharides existing in nature, therefore can be suitably and economically used as the chemical feedstocks.
The production of furans and furan derivatives from sugars has attracted increasing attention in chemistry and in catalysis studies, and is believed to have the potential to provide one of the major routes to achieving a sustainable energy supply and source of chemicals production. Indeed, dehydration and/or oxidation of the sugars available within biorefineries with integrated biomass conversion processes can lead to a large family of products including a wide range of furans and furan derivatives.
Among the furans having the most commercial values, furan-2,5-dicarboxylic acid (also known as 2,5-furandicarboxylic acid, hereinafter abbreviated as FDCA) is a valuable intermediate with various uses in several industries including pharmaceuticals, pesticides, antibacterial agents, fragrances, agricultural chemicals, as well as in a wide range of manufacturing applications of polymer materials, e.g. bioplastic resins. As such, FDCA is considered a green alternative of terephthalic acid (TA), a petroleum-based monomer that is one of the largest-volume petrochemicals produced yearly worldwide. In fact, the US Department of Energy has identified FDCA as one of the top 12 priority compounds made from sugars into a value-added chemical for establishing the “green” chemistry of the future, and as such, it has been named one of the “sleeping giants” of the renewable intermediate chemicals (Werpy and Petersen, Top Value Added Chemicals from Biomass. US Department of Energy, Biomass, Vall, 2004).
Although various methods have been proposed for commercial scale production of FDCA (for review, see, e.g., Tong et al., Appl. Catalysis A: General, 385, 1-13, 2010), present methods of synthesizing FDCA rely on the chemical dehydration of hexoses, such as glucose or fructose, to the intermediate 5-hydroxymethylfurfural (5-HMF), followed by a chemical oxidation to FDCA. During this oxidation HFCA (2-hydroxymethyl 5-furan carboxylic acid), or FFCA (2-formyl-5-furan carboxylic acid) are produced as transient intermediates (van Putten, R-J et al., Chem Rev. 2013, 113(3), 1499-1597). However, current FDCA synthesis processes via dehydration of fructose have many drawbacks. For example, fructose is produced from the enzymatic isomerization of glucose, and as a result, a mixture of glucose and fructose is produced, requiring fructose to be separated before chemical dehydration. Furthermore, the high degree of freedom of the fructose molecule produces a number of other byproducts and, as a result, optimizing its dehydration to produce HMF in high yields remains challenging (especially when inexpensive conditions amenable to scale up are required). Thus, the primary technical barrier in the production and use of FDCA is the development of an effective and selective dehydration process from biomass-derived sugars.
Other chemicals exist that can be obtained from the conversion of glucose, by either chemical or enzymatic means, such as 2-ketogluconate, 5-ketogluconate, or 2-dehydro-3-deoxygluconate (DHG). But there are no methods available for the efficient conversion of these compounds into 2-formyl-5-furan carboxylic acid (FFCA) or 3-dehydro-5-furan carboxylic acid (HFCA), or further into the more valuable 2,5-furan dicarboxylic acid (FDCA).
It is therefore desirable to develop methods for production of FDCA and FDCA precursors, as well as many other chemicals and metabolites, by alternative means that not only would allow for the substitution of renewable feedstocks for petroleum-based feedstocks, but also use less energy and capital-intensive technologies. In particular, intermediate processes for transforming abundant sugars into precursors that could be readily converted into FDCA would be a very powerful technology, leading to inexpensive production of this valuable chemical as well as other carboxylic acids.